1. Field of the Invention
This invention relates generally to superabrasive inserts, or compacts, for abrasive cutting of rock and other hard materials. More particularly, the invention pertains to improved interfacial geometries for polycrystalline diamond compacts (PDCs) used in drill bits, reamers, and other downhole tools used to form bore holes in subterranean formations.
2. Background of Related Art
Drill bits for oil field drilling, mining and other uses typically comprise a metal body into which cutters are incorporated. Such cutters, also known in the art as inserts, compacts, buttons and cutting tools, are typically manufactured by forming a superabrasive layer on the end of a sintered carbide substrate. As an example, polycrystalline diamond, or other suitable abrasive material, may be sintered onto the surface of a cemented carbide substrate under high pressure and temperature to form a PDC. During this process, a sintering aid such as cobalt may be premixed with the powdered diamond or swept from the substrate into the diamond. The sintering aid also acts as a continuous bonding phase between the diamond and substrate.
Because of different coefficients of thermal expansion and bulk modulus, large residual stresses of varying magnitudes and at different locations may remain in the cutter following cooling and release of pressure. These complex stresses are concentrated near the diamond/substrate interface. Depending upon the cutter construction, the direction of any applied forces, and the particular location within the cutter under scrutiny, the stresses may be either compressive, tensile, or shear. In the diamond/substrate interface configuration, any nonhydrostatic compressive or tensile load exerted on the cutter produces shear stresses. Residual stresses at the interface between the diamond table and substrate may result in failure of the cutter upon cooling or in subsequent use under high thermal or fractional forces, especially with respect to large-diameter cutters.
During drilling operations, cutters are subjected to very high forces in various directions, and the diamond layer may fracture, delaminate and/or spall much sooner than would be initiated by normal abrasive wear of the diamond layer. This type of premature failure of the diamond layer and failure at the diamond/substrate interface can be augmented by the presence of high residual stresses in the cutter.
Typically, the material used as a substrate, e.g., carbide such as tungsten carbide, has a higher coefficient of thermal expansion than diamond matrix. This mismatch of coefficients of thermal expansion causes high residual stresses in the PDC cutter during the high-pressure, high-temperature manufacturing process. These manufacturing induced stresses are complex and of a non-uniform nature and thus often place the diamond table of the cutter into tension at locations along the diamond table/substrate interface.
Many attempts have been made to provide PDC cutters which are resistant to premature failure. The use of an interfacial transition layer with material properties intermediate of those of the diamond table and substrate is known within the art. The formation of cutters with non-continuous grooves or recesses in the substrate filled with diamond is also practiced, as are cutter formations having concentric circular grooves or a spiral groove.
The patent literature reveals a variety of cutter designs in which the diamond/substrate interface is three dimensional, i.e., the diamond layer and/or substrate have portions which protrude into the other member to xe2x80x9canchorxe2x80x9d it therein. The shape of these protrusions may be planar or arcuate, or combinations thereof.
U.S. Pat. No. 5,351,772 of Smith shows various patterns of radially directed interfacial formations on the substrate surface; the formations project into the diamond surface.
As shown in U.S. Pat. No. 5,486,137 of Flood et al., the interfacial diamond surface has a pattern of unconnected radial members which project into the substrate; the thickness of the diamond layer decreases toward the central axis of the cutter.
U.S. Pat. No. 5,590,728 of Matthias et al. describes a variety of interface patterns in which a plurality of unconnected straight and arcuate ribs or small circular areas characterizes the diamond/substrate interface.
U.S. Pat. No. 5,605,199 of Newton teaches the use of ridges at the interface which are parallel or radial, with an enlarged circle of diamond material at the periphery of the interface.
In U.S. Pat. No. 5,709,279 of Dennis, the diamond/substrate interface is shown to be a repeating sinusoidal surface about the axial center of the cutter.
U.S. Pat. No. 5,871,060 of Jensen et al., assigned to the assignee hereof, shows cutter interfaces having various ovaloid or round projections. The interface surface is indicated to be regular or irregular and may include surface grooves formed during or following sintering. A cutter substrate is depicted having a rounded interface surface with a combination of radial and concentric circular grooves formed in the interface surface of the substrate.
Drilling operations subject the cutters on a drill bit to extremely high stresses, often causing crack initiation and subsequent failure of the diamond table. Much effort has been devoted by the industry to making cutters resistant to rapid deterioration and failure.
Each of the above-indicated references, hereby incorporated herein, describes a three-dimensional diamond/substrate interfacial pattern which may accommodate certain of the residual stresses in the cutter. Nevertheless, the tendency to fracture, defoliate and delaminate remains. An improved cutter having enhanced resistance to such degradation is needed in the industry.
The present invention provides a drill bit cutter having a diamond/substrate interface which has enhanced resistance to fracture, defoliation, and delamination. The invention also provides a cutter with a pattern which helps to break up and isolate the areas of high residual stress throughout the interfacial area and having the diamond table with a reduced stress level. The invention still further provides a cutter with enhanced bonding of the diamond table to the substrate.
The invention comprises a cutter having a superabrasive layer overlying and attached to a substrate. The interface between the superabrasive layer and the substrate is configured to enable optimization of the radial compressive prestressing of the diamond layer or table. The interface configuration preferably incorporates a three-dimensional interface having radial members or ribs and at least one generally annular member such as a circular or polygonal member, or an irregularly shaped annular member comprising a combination of curved and straight geometrical segments, arranged in a preselected pattern. Preferably, the radial and non-radial members are interconnected at junctions therebetween such that the diamond table is in nearly uniform radial and circumferential compression. Thus, the desired lowering of the high residual stress of the diamond table within the interior and exterior thereof results in a biaxial compressive prestress and in the vicinity of the interface occurs upon cooling from a high-temperature, high-pressure manufacturing procedure used in forming the cutter.
A decrease in residual radial and circumferential compressive prestress of the diamond table along at least the interface of the table and the substrate counteracts the forces superimposed upon the table during drilling or when conducting other downhole operations, depending on the tool in which the cutter is mounted. The resistance to delamination is also increased.